function lazyload(){
    let temp1=window.innerHeight||document.documentElement.clientHeight
    let temp2=document.body.scrollTop||document.documentElement.scrollTop
    let maxShowHeight=temp1+temp2
    let imgs=document.querySelectorAll("img")
    imgs.forEach(function(item,i){
       console.log(item,item.offsetTop,maxShowHeight);
        if(item.offsetTop<maxShowHeight){
            item.src=item.getAttribute('src-real')
        }
    })
    
}
let t=null
lazyload()
window.onscroll=function(){
    if(t)clearTimeout(t)
    t=setTimeout(()=>{
        lazyload()
    },50)
}